2 Dimensional Shapes 2
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Transcript of 2 Dimensional Shapes 2
10/4
10/4
Bell Activity: How many triangles are there in this diagram?
Two Dimensional Shapes
Learning objectives
• Be able to find the area and circumference of a circle
The perimeter of this shape has a special name. What is it?
My perimeter is calledThe Circumference
These things are very important in calculating the circumference of a circle.
Remember a round pi (spelled wrong)
Pi
Pi is a large number that goes on forever
But we use 3.14 to be approximately equalto pi.
r
d
r = radiusd = diameter
To calculate the circumference of a circleYou do3.14 x dOr2 x 3.14 x r Look at Mr Lock’s example on the board.
Use your calculator to calculate the circumference of these shapes
To calculate the circumference of a circleYou do3.14 x dOr2 x 3.14 x r
11cm
3cm
1.56cm
This circle has circumference 298cm².
What do you think it’s diameter is?
It’s radius?
Area of a circle
• For this, you have to know the radius
• The area is given by
• A = π X r²
• (remember to square the radius before multiplying)
Try these
5cm
2.5cm
13cm
Find the area of this shape…
24.6cm
How the heck would you do this then?
• 5 mins. Like an exam
I want an answer
What
Would
You
Do?
12cm
4cm
Find the area….. (435 marks)
Without looking back, write down how you construct a triangle using ruler and compasses
Now write down 6 quadrilaterals (and how to find their area)